The appearance inspection of a tire is important in checking for the presence of defects on the tire which has been cure-molded into a product. For example, it is necessary to inspect the inner surface of a tire closely since the defects thereon cannot be visually checked after it is fitted on the wheel.
Conventionally, the tire inner surface Ts has been closely inspected for molding defects and the like, using a tire inspection apparatus as shown in FIG. 14. In carrying out the inspection, cameras 11 to 13 as the image shooting means and laser beam generators 21 to 23 as the illuminating means casting slit light 21a to 23a are disposed in the center opening space of a tire T rotating circumferentially, and the images of portions on the tire inner surface Ts illuminated by the slit light 21a to 23a are shot by the cameras 11 to 13.
For example, three cameras 11 to 13 shooting the images of the inner surface Ts of a tire are set with image shooting orientations such that they can capture the images of different regions, namely, one tire side T1, the tire center T2, and the other tire side T3 of the tire inner surface Ts. Further, since the cameras 11 to 13 are located within the limited space of the tire center opening, the cameras 11 to 13 are so arranged as to have their respective shooting directions relatively displaced from each other circumferentially, as shown in FIG. 15, and also set for the respective shooting positions different from each other in the axial direction of the tire, which is a direction perpendicular to the tire inner circumference. For example, let the shooting direction of the camera 12 be the reference position in the circumferential direction. Then the cameras 11 to 13 may be arranged compactly such that the shooting direction of the camera 11 is displaced by angle α in the circumferentially counterclockwise direction and the shooting direction of the camera 13 is displaced by angle β in the circumferentially clockwise direction.
Laser beam generators 21 to 23 are provided for the cameras 11 to 13, respectively, and they cast slit lights 21a to 23a corresponding to the image shooting orientations. More specifically, the slit lights are cast in the radial directions of the tire such that the slit light 21a cast from the laser beam generator 21 is directed to one tire side T1, the slit light 22a cast from the laser beam generator 22 to the tire center T2, and the slit light 23a cast from the laser beam generator 23 to the other tire side T3. With the cameras 11 to 13 shooting the images of the portions on the tire inner surface Ts illuminated by the slit lights 21a to 23a, the images of surface unevenness, such as defects and mold marks, on the tire inner surface Ts are captured.
The shot image data obtained by the cameras 11 to 13 are outputted to preprocessing means 31 to 33, which are, for instance, computers, connected to the respective cameras. The preprocessing means 31 to 33 perform a preprocessing, which is a processing of the image data, when image shooting for full tire circle or over is completed. As a result of this preprocessing, the shot images P1 to P3 of the respective regions are obtained. The shot images P1 to P3 thus obtained are outputted to the control means 46, which is a computer connected individually to the preprocessing means 31 to 33, whenever a preprocessing is completed.
The control means 46 to which the shot images P1 to P3 are inputted controls the inspection in all aspects, and a keyboard 35 as an input means and a monitor 36 as a display means are connected thereto.
Inputted through the keyboard 35 are information on the size of the tire T to be inspected and the like and the displacement angles α and β for the arrangement of the cameras 11 to 13.
Also, displayed on the monitor 36 are an image synthesized by the image synthesizing means 40 of the control means 46 to be discussed later, an acceptability determination result of the tire T as determined by the acceptability determining means 47, and the like.
The control means 46 is roughly constituted of an image synthesizing means 40, a camera position storage means 44, and an acceptability determining means 47.
The control means 46, which is connected to a motor drive means 51 for controlling the drive of a motor 52 via a drive signal line 70, controls the rotation or the stop of a rotating table 53 which rotates, driven by the motor 52. Further, the control means 46 is connected to the camera 11 and the laser beam generator 21 for shooting the image of the tire side T1 via a shooting signal line 71, to the camera 12 and the laser beam generator 22 for shooting the image of the tire center T2 via a shooting signal line 72, and to the camera 13 and the laser beam generator 23 for shooting the image of the tire side T3 via a shooting signal line 73. Thus, the control means 46 outputs shooting start signals for starting image shooting and shooting end signals for ending image shooting through the respective shooting signal lines 71 to 73.
The camera position storage means 44 stores the relative displacements in the circumferential direction of the cameras 11 to 13, more specifically, the displacement angle α between the cameras 11 and 12 and the displacement angle β between the cameras 12 and 13.
The image synthesizing means 40, which includes a circumferential position aligning means 41, an overlap synthesizing means 42, and a processing means 43, synthesizes the images captured by the cameras 11 to 13.
The circumferential position aligning means 41 reads out the circumferential displacement angles α and β resulting from the arrangement of the cameras 11 to 13 from the camera position storage means 44, shifts the shooting start positions S1 to 83 for the respective images in accordance with the read-out displacements of angles α and β, and align the positions thereof such that it looks as though the cameras 11 to 13 have started shooting simultaneously.
The overlap synthesizing means 42 superimposes the shot images by detecting protruding portions 15 called ridges from the overlap of adjacent images, out of the shot images aligned by the circumferential position aligning means 41, and performing a pattern matching thereof. Note that the “ridges” as used herein are periodically-occurring protruding portions 15 which are formed on the tire inner surface Ts in the process of tire building. They are a transfer of air purge grooves formed at intervals on the surface of the bladder for giving pressure to the tire inner surface Ts in the cure-molding of a tire T.
The processing means 43 processes the images pattern-matched by the overlap synthesizing means 42 into a synthesized image PP for full tire circle before outputting it to the acceptability determining means 47.
The acceptability determining means 47 determines whether there are any tire-building defects or marks on the tire inner surface Ts resulting from cure-molding. This is done by performing an image processing on the surface unevenness of the tire inner surface Ts, using the synthesized image PP synthesized by the processing means 43.
Conventionally, an inspection is carried out as shown in FIG. 16 using an inspection apparatus of a structure as described above.
At time t0, the first tire T for the initial inspection begins rotating as the rotating table 53 rotates at a rotation start signal outputted from the control means 46. At the same time, a shooting start signal is outputted, and slit lights 21a to 23a are cast to the tire sides T1 and T3 and the tire center T2, respectively, from the laser beam generators 21 to 23. And all the cameras 11 to 13 begin shooting the illuminated portions simultaneously. It is to be noted, however, that, relative to the shooting position of the camera 12, the camera 11 begins shooting at a position angle α ahead (phase difference) in the direction of tire rotation G, and the camera 13 at a position angle β behind (phase difference) in the direction of tire rotation G. The shot image data obtained by the cameras 11 to 13 are successively outputted to the preprocessing means 31 to 33.
At time t1, when a predetermined shooting time A1, equal to full tire circle or over, has elapsed from the start of shooting at time t0, the control means 46 outputs a rotation stop signal to end the rotation of the tire T to the motor drive means 51 and a shooting end signal to end the shooting to all the cameras 11 to 13 and all the laser beam generators 21 to 23. With the image shooting by all the cameras 11 to 13 completed, the preprocessing means 31 to 33 immediately starts a preprocessing, the procedure of processing the captured image data.
At time t2, after the end of image pickup by all of the cameras 11 to 13 and using the time when the preprocessing means 31 to 33 undertake the preprocessing, the first tire T on the rotating table 53 is replaced by the second tire T to be inspected next. Also, preparation for an immediate start of the next shooting is made by making certain that the cameras 11 to 13 and the laser beam generators 21 to 23 are in predetermined positions within the tire center opening.
Then, at time t3, the preprocessing for the tire side T1 of the first tire is completed in the preprocessing time B1. Next, at time t4, the preprocessing for the tire side T3 is completed in the preprocessing time B3. Finally, at time t5, the preprocessing for the tire center T2 is completed in the preprocessing time B2. Thus the preprocessing for the first tire T is completed. Then the control means 46 performs a control such that all the cameras 11 to 13 start shooting simultaneously with the rotation of the second tire T. At time t6, when the predetermined shooting time A1, equal to full tire circle or over, has elapsed from the start of shooting at time t5, the control means 46 outputs a rotation stop signal to end the rotation of the tire T to the motor drive means 51 and a shooting end signal to end the shooting to all the cameras 11 to 13 and all the laser beam generators 21 to 23. With the image shooting by all the cameras 11 to 13 completed, the preprocessing means 31 to 33 immediately starts a preprocessing, the procedure of processing the shot image data.
At time t7, after the end of shooting by all of the cameras 11 to 13 and using the time when the preprocessing means 31 to 33 undertake the preprocessing, the second tire T on the rotating table 53 is replaced by the third tire T to be inspected next. Also, preparation for an immediate start of the next shooting is made by making certain that the cameras 11 to 13 and the laser beam generators 21 to 23 are in predetermined positions within the tire center opening.
Then, the preprocessing for the tire side T1 of the second tire is completed in the preprocessing time B1. Next, the preprocessing for the tire side T3 is completed in the preprocessing time B3. Finally, at time t8, the preprocessing for the tire center T2 is completed in the preprocessing time B2. Thus the preprocessings for the second tire T are completely finished. By repeating this procedure, the inspections of the tire inner surfaces are carried on successively.
It is to be noted that the differences between the preprocessing times B1, B2, and B3 result from the differences in the size of image shooting range. The preprocessing time B1 is the shortest because the tire side T1 is located on the tire side placed on the table such that the deflection in the tire side T1 disappears, thus making the image shooting range planar. The preprocessing time B3 is the second shortest because the tire side T3 has a rounded image shooting range. The preprocessing time B2 is the longest because the tire center T2 has the widest image shooting range.
The shot images P1 to P3, which have undergone image shooting and preprocessing through the above-described procedures, are outputted individually to the image synthesizing means 40 of the control means 46 immediately after the completion of preprocessing. As soon as the shot images P1 to P3 are all ready, the image synthesizing means 40 carries out a synthesizing process as illustrated in FIGS. 17A to 17D.
Firstly, as shown in FIGS. 17A and 17B, the shooting start positions S1 to S3 of the shot images P1 to P3 are shifted by the circumferential position aligning means 41 by as much as the positional displacement angles α and β (phase differences) of the shooting directions of the cameras 11 to 13. More specifically, relative to the shooting start position S2 of the shot image P2, the shooting start position S1 of the shot image P1 is shifted by as much as the angle α, and the shooting start position S3 of the shot image 23 is shifted by as much as the angle β. In this manner, the position alignment is accomplished such that it looks as though all the cameras 11 to 13 have started shooting at the same circumferential position.
Next, as shown in FIG. 17C, the overlaps of the shot images P1 to P3 shot by the cameras 11 to 13 are synthesized by pattern matching by the overlap synthesizing means 42. More specifically, the shot images P1 to P3 are synthesized by pattern-matching the overlap Q1 of the shot images P1 and P2 and the overlap Q2 of the shot images P2 and P3. In the pattern matching, protruding portions 15 formed at intervals in the shot images P1 to P3 are identified therefrom, and then the protruding portions 15 are matched up with each other.
Next, as shown in FIG. 17D, the processing means 43 extracts a synthesized image equal to full tire circle, relative to the shooting start position S3 of the camera 13, by deleting the remaining unnecessary portions. Thus, the images of the tire inner surface Ts for full tire circle are processed as the synthesized image PP. And after the synthesized image PP is checked for acceptability by the acceptability determining means 47, both the synthesized PP and the result of acceptability determination of the tire inner surface Ts resulting from tire building are outputted to the monitor 36 for display.
However, in the structure as described above, the three cameras 11 to 13 are so set as to shoot the images simultaneously as shown in FIG. 15 and FIG. 16. Then, even when the same shooting time A1 is applied to the cameras 11 to 13, the time required for preprocessing will vary with the regions shot if the imaging region of the tire center T2 shot by the camera 12 is wider than the others. As a result, when a preparation is made for the next inspection by placing the next tire T on the rotating table 53 after the end of image shooting by all of the cameras 11 to 13, the cameras 11 and 13 must wait for the completion of preprocessing for the tire center T2. Thus result the waiting times C1 and C2, which can be a waste of time.
For example, the waiting times C1 and C2 are each about 5 or 6 seconds. Yet, a simple calculation on the assumption that about 8,000 tires are inspected per day points to the waiting time of about 11 hours per day. This is an impediment to the improvement of inspection efficiency, and there really exists a need for an efficient method for image shooting and processing.
Also, the shot images P1 to P3 preprocessed by the preprocessing means 31 to 33 are outputted to the control means 46 in nearly the same timing. Hence, there occurs a concentration of load in the network connecting the control means 46 and the preprocessing means 31 to 33. This causes a longer time for transfer of the shot images P1 to P3, which occasionally results in waiting for the transfer or the like. This is also an impediment to smooth performance of inspection of the next tire T.
Further, an inspection by a single session of image shooting does not necessarily result in a successful image shooting of the tire inner surface Ts. There are often image shooting failures, with one of the cameras 11 to 13 developing malfunction. There are even cases of multiple shootings necessitated.
For example, as shown in FIG. 18, if a trouble of image shooting of the tire side T1 (X marked) occurs at time E1 after the start of shooting in the inspection of the first tire T, it will be necessary to carry out the shooting by all of the cameras 11 to 13 again from time E1. Then all the shot image data for the shooting time H on the tire center T2 and the tire side T3 will go to waste.
Moreover, the conventional method for image synthesis is valid when the graphic part for pattern matching is sufficiently large in comparison with the size of the image to be synthesized. Yet, when the protruding portions 15 on the tire inner surface Ts, for instance, are used as the graphic for pattern matching, the interval between the protruding portions 15 is relatively short for the circumferential length of the tire T. As a result, disagreement can often occur in the relationship between the shooting directions of the cameras and the shooting start positions S1 to S3 of the images captured. Thus, if there actually is disagreement between the shooting start positions S1 to S3 and the shooting directions, pattern matching of protruding portions 15 staggered by a single section can occur in the synthesis of the shot images P1 to P3 by the overlap synthesizing means 42 as shown in FIG. 19. Therefore, it is possible that the image of a non-defective tire T is synthesized into an image of a defective tire at the stage of image analysis.
Also, as shown in FIG. 15, the images are synthesized from the shooting start positions S1 to S3 of shot images and the relative displacement angles α and β of the cameras 11 to 13. Hence, it is necessary to carry out shootings for full tire circle or over if shot images for full tire circle are to be obtained with certainty. This means unnecessary portions of time spent in the image shooting time and preprocessing time.
For example, Patent Document 1 discloses a technology of image shooting by CCD cameras, which are a plurality of image shooting means arranged with circumferential position displacements, while slit lights are cast to the tire inner surface.
According to the method of Patent Document 1, however, the inspection of the tire inner surface is performed by comparing the images of individual regions shot by the plurality of image shooting means against the master images of the tire inner surface prepared in advance. This requires extra trouble since the master images of the tire inner surface to be inspected must be prepared in advance. Also, tires having undergone the tire-building process have individual differences on the tire inner surface such that comparison with the master images cannot assure accurate inspection of the tire inner surface because of the individual differences.
Also, Patent Document 2 discloses a technology for image processing through pattern matching of shot images. In this technology of judging raised letter information through pattern matching, raised letters formed on the tire side at the time of cure-molding, for instance, are shot with a camera, the raised letters are read by a processing means from the shot image, and the raised letters are compared with a master image stored in the processing means in advance.